The Christmas holidays are kicking off with good weather as parts of the South Island are set to see higher than average temperatures this week – with areas of Otago reaching 30 degrees Celsius.

New Zealand's weather will be dominated by a ridge of high pressure for the next few days, says a MetService spokesperson.

On Tuesday, isolated thunderstorms are possible in northern inland areas of the South Island.

'A subtropical low approaching from the north is now expected to stay well away from the country, with minimal risk of severe weather as it passes by on Tuesday and Wednesday,” says MetService forecaster Sonja Farmer.

"However, for most of the South Island temperatures will be 'on par” for the time of the year. We've got some really warm temperatures later in the week.

"By Thursday, Wānaka and Alexandra are expected to see highs of 30C. Gore could reach 27C and Dunedin 26C. Parts of Otago, including Lake Hawea, will see higher than average temperatures this week," says Sonja.

"In Canterbury, Ashburton could reach 30C, markedly above the 21C that is normal for this time of year. Christchurch will see highs of 28C, while in Kaikōura it could reach 26C."

Thursday will see some rain over Stewart Island and in Fiordland but the rest of the South Island will be dry.

A severe thunderstorm watch was issued for parts of the North Island on Christmas Day.

People in Bay of Plenty, Taupo, Gisborne, Hawkes Bay and Taihape were told to expect scattered thunderstorms, with localised heavy rain and small hail.